How Weather Can Affect Horses At The Kentucky Derby

Known for bluegrass, bourbon and horse racing, Kentucky is home to one of the most memorable sporting events of the year, quite literally living up to its reputation as the “most exciting two minutes in sports.” The 2025 Kentucky Derby is Saturday, May 3, in Louisville, Kentucky, held annually on the first weekend of May.

The Kentucky Derby, first held on May 17, 1875, is one of the oldest major sporting events in the U.S. held annually since its inception, and is the first leg in the Triple Crown (followed by the Preakness Stakes in Baltimore and the Belmont Stakes in Belmont Park, New York).

In the Derby, the horses will run 1 and a quarter miles – you may also hear it referred to as 10 furlongs, the equivalent of 660 feet each. The Kentucky Oaks, held the Friday before the Kentucky Derby, is a gender-specific race where 3-year-old fillies (female horses) compete in a 1-and-an-eighth-mile race. The Derby is open to eligible colts, geldings or fillies.

But did you know? Weather conditions during the Kentucky Derby will impact more than just the festivities – it can impact horse performance, giving an edge to an unlikely candidate to win.

So if you plan to attend, place a bet or host a watch party while you cheer on your favorite horse during the Kentucky Oaks and Kentucky Derby, there are a few things you need to know as you gear up for the racing weekend. We’re highlighting a few ways that weather can directly impact the race track and horse performance, as well as a few important terms you may hear.

2025 Kentucky Derby Forecast

It’s a little too soon to know exactly how the weather will shape up for the 2025 Kentucky Derby, but with our 10-day forecast for Louisville, Kentucky, you’ll know in advance what kind of sunny, cloudy or rainy day odds are on the table.

From 2020 through 2023, weather conditions remained relatively comfortable, with highs hovering around the mid-70s, and sunny to cloudy conditions. It was quite warm, though cloudy, in 2024, with highs in the 80s.

The wettest Derby was in 2018 with over 3 inches of rain; Justify went on to win in sloppy conditions.

How Weather Can Affect The Horses At The Kentucky Derby

We know how hot and cold affect us during seasonal changes, so it’s no surprise that horses, livestock and pets will react (both positively and negatively) to certain weather conditions.

This will be important for your winning pick because their conditioning training could just mean a “nose” of difference at the finish line. And for trainers and jockeys, this would mean navigating some tricky side effects from weather conditions.

1. Cold weather conditions

In my experience, my gelding strongly prefers cool to cold weather compared to hot and muggy conditions. Ironically, the horses at our barn tend to be more “hot” in cool weather, meaning they are more likely to be excitable, forward and fresh, especially if they’ve been stalled with limited turnout (also known as time out in a pasture).

For horses that have been clipped or shaved, they will begin to feel cold when temperatures hit 40 degrees. Add in the wind chill and rain, and a horse will struggle to maintain body heat.

Side effects of cold weather conditions include shivering, muscle stiffness, increased heart rate, cold extremities, respiratory problems and weight loss.

For a performance animal like a Thoroughbred that may commonly have sensitivities to weather conditions, cold symptoms like muscle pain, problems breathing and weight loss can be extremely detrimental to their health.

2. Hot weather conditions

Just like people (and unlike dogs), horses will sweat for “evaporative cooling,” as well as through dilation of the capillaries in the skin to dissipate warmth. The more a horse exercises, the more internal heat is generated by their muscles.

And similar to people, horses can become seriously dehydrated when they sweat and exercise too long without hydrating and replenishing their fluids properly. Heat exhaustion (also known as heat stress) can be life-threatening when a horse is unable to cool itself off by sweating.

When their core temperature reaches 104 degrees, metabolic systems, organs and circulatory systems will begin to shut down.

On race day, it’s important to pay attention to the Equine Heat Index – when temperatures rise above 80 degrees, there's a higher risk of heat-related illnesses.

3. Humidity levels

Strenuous workouts when the humidity is high is just asking for trouble. When the combined air temperature and relative humidity exceeds 150, the horse will have difficulty sweating and cooling down. If you see a horse no longer sweating (or sweating only a little) despite high heat and humidity, that’s a bad sign.

Core body temperatures of Thoroughbred racehorses can increase rapidly during a race, at almost 2 degrees per minute, and rising above a certain threshold can lead to dangerous heat illness.

Since horses typically have low tolerance for high humidity, it may also increase their susceptibility to respiratory disease.

4. Air pressure

Changes in barometric pressure, such as temperature drops prior to a big storm, can cause some horses to experience mild to severe colic (abdominal pain in horses, which may require surgery). While barometric changes on their own might not always trigger colic, when combined with dehydration, environmental changes and exercise, it could certainly be a recipe for illness.

5. Wind speed

Imagine big gusts of wind pelting you as you run during a race – whether it’s whipping dirt into your eyes, or strong enough to get you off balance, it’s going to affect your performance.

When winds blow down the stretch (meaning the wind is in their face), horses in the front will be exerting a lot more effort to move forward at speed, while the horses behind them take advantage of the windbreak.

This is why if you see a horse break early to the front, it could mean they wipe out through exertion early on – and may not cinch the win.

6. Pollen count

As ridiculous as it might seem, this spring season has seen an explosion in pollen count, so don’t discount how a horse will react to the sudden influx. My gelding, who has never suffered much from allergies in the past, has been suddenly overcome with snot, sneezing and coughing. During our training, any dust-up of pollen and dirt will send him into giant coughs and sneezes, practically launching me out of the saddle during our trot.

Seasonal allergies can cause allergic reactions in horses, from biting flies and mold to pollen and dust. Symptoms of allergic reactions can include raised bumps, coughing, runny nose and exercise resistance.

If horses are trained in areas with lower pollen counts, I wouldn’t be surprised to see the horses having a tough time as they head to Louisville for the Derby.

(READ MORE: Best Pollen Air Purifiers of 2025)

How Weather Impacts Track Conditions

Outside of the horse’s stamina, health and weight, track type and conditions will play a huge part in the race day performance. From breeding to training, turf and dirt horses will have wildly different experiences on ground conditions.

Track types: Turf and dirt

Originally, the U.S. only had oval dirt tracks, whereas turf racing was much more popular in Europe, but now both track options have flourished.

Trainers will look at a variety of criteria to determine the horse’s racing preference, from foot size (such as a larger hoof called a “grass foot”), pedigree, body build, distance ability and how they handle kickback on a dirt surface, just to name a few.

Horse performance qualifications based on track type:

• Turf tracks require horses to be agile, with quick bursts of speed and sharp turns, with the ability to maintain balance on the softer footing.
• Dirt tracks require power and endurance, with the soil surface more compact. It requires a fast pace, handling dust kick up, and more brute strength over longer distances.

1. Dry or firm

Moisture composition in the footing will affect how the surface gives under the hooves. If the dirt is too loose, it can slow down the horses, and if maintained too firm, it will be hard to grip as the horse launches forward.

For turf, this could be problematic, as firm, hard turf will have the horses working harder than horses that prefer standard turf conditions.

2. Some precipitation

When there’s some moisture in the ground, the softer the impact will be on the horse, especially on turf. Some moisture may be ideal for some horses, since the turf and dirt race tracks at Churchill Downs are designed for water runoff.

3. Wet and soggy

Rain can have a big impact on ground conditions. The more moisture in the ground, the softer it is, and the deeper the track, the more likely a horse is to sustain soft tissue damage.

Just like a human running on soft sand, the horse will move more slowly, with more energy wasted and more stress on muscles and joints. Add the spray of mud and water, and the jockeys will not be having a good time.

Likewise, a lot of rain will have softened the turf, and you may hear the condition change from “firm” to “yielding” or “soft.” This will mean horses that prefer to run on firm turf will face some challenges since softer footing will exhaust them faster.

There’s a silver lining, however, for those horses that prefer muddy or “sloppy” track conditions, and those that favor wet surfaces over firm.

4. Raining

Active rain will affect both horses and jockeys in critical ways. Besides affecting the track conditions of both turf and dirt, rain will decrease visibility, maneuvering and grip. Whether it’s bumping into other horses or becoming off-balance, at best the rain could cost them the race – at worst, it could mean injury.

5. Synthetic or “all-weather” track

Synthetic track options include Polytrack and Tapeta, which had become popular in the mid-2000s, but some popular tracks like Santa Anita and Keeneland have since returned to dirt. Polytrack is more commonly found in England.

The difference lies in the surface, with some synthetic tracks made of silica sand and fibers (like recycled carpet), while others are made of rubber fiber. The surface is then coated in wax and laid over a gravel base underneath to allow water to drain more easily.

Watching The 2025 Kentucky Derby

As we look ahead to the Kentucky Derby, it's clear that weather conditions will play a crucial role in both the preparation and performance of these elite Thoroughbreds. From temperature fluctuations and humidity levels to track conditions and seasonal allergies, trainers and fans must carefully consider these environmental factors when developing their race-day strategies.

Be sure to monitor weather forecasts closely as the Derby approaches. It’s critical to consider how each horse has performed under similar conditions, since even the most talented horse can be affected by extreme temperatures.

So whether you're a racing enthusiast, a bettor or just someone attending a Derby-themed party, factoring in these weather-related variables could make the difference between picking a winner or watching your favorite falter down the stretch at Churchill Downs.

After all, in the "most exciting two minutes in sports," every environmental factor counts, and the weather often has the final say in how the day unfolds.